Apparatus for deriving information concerning the movements of a vehicle

ABSTRACT

The invention provides an apparatus for deriving information concerning the movement of a road vehicle. In a preferred example a single microwave source is mounted under the vehicle to illuminate the road surface. Two receiving ports are provided, one to receive energy reflected from the illuminated surface to one side of the center line of the vehicle and the other to receive energy reflected from the illuminated surface to the other side of the center line. The two Doppler shifts are determined and compared to determine if there is a difference which indicates that the vehicle is turning, the sign of any difference indicating the direction of turn. One of the Doppler signals is shaped and counted to provide an indication of the speed of the vehicle and one of the Doppler signals is processed to provide an indication of forward or reverse motion.

This invention relates to apparatus for deriving information concerningthe movement of a vehicle over a surface. In particular, the inventionis concerned with apparatus for deriving such information for use invehicle location systems such as are the concern of our co-pendingapplication Ser. Nos. 606,955 and 584,596, now respectively U.S. Pat.Nos. 3,947,807 of Mar. 30, 1976 and 3,984,806 of Oct. 5, 1976.

In both of the inventions in our co-pending applications mentionedabove, information is required to be derived concerning the distancetravelled by a vehicle and the extent and direction of any turn whichthe vehicle may make. In a practical system applied to a wheeled roadvehicle the required distance log and turn indicator have beenelectro-mechanical in nature relying on the one hand on being driven insynchronism with the road wheels of the vehicle and on the other handupon being turned as the steering gear of the vehicle is turned. The useof such electro-mechanical devices does, however, involve a number ofpractical disadvantages. Because of their moving parts, maintenance isrequired and mechanical wear must, of course, be expected. In addition,such factors as tire wear, tire pressures and the extent of slip betweenthe wheel and the road surface contribute to inaccuracies in theinformation signals which are produced. As is well known, the extent towhich a vehicle turns off-course does not bear a constant relationshipwith the extent to which the steering gear is turned, but, varies withsuch factors as speed and the condition of the road surface.

A principal object of this invention is to provide an improved apparatusin which the extent to which reliance need be placed uponelectro-mechanical devices for deriving the basic turn and/ordistance-travelled information is reduced.

According to this invention, an apparatus for deriving informationconcerning the movements of a surface-borne vehicle comprises means forilluminating the surface over which the vehicle is to travel withelectro-magnetic energy, means for receiving reflected electro-magneticenergy from a portion of said illuminated surface to one side of a lineextending along the length of said vehicle, means for receivingelectro-magnetic energy from another portion of said illuminated surfaceto the other side of said line, means for deriving the Doppler frequencycomponents in the energy received by each receiving means and means forutilising said two Doppler frequency components to provide informationconcerning the movement of said vehicle over said surface.

The term "surface-borne vehicle" is used to denote a vehicle whichtravels in contact with or in close proximity to the earth's surface,i.e. water craft, land craft and hovercraft, as distinct from aircraftor space craft.

Whilst the information provided may be ulilised in a variety of ways,preferably said apparatus forms part of a system for indicating theposition of the vehicle, whilst travelling over a predetermined networkof routes. In particular, the system is preferably in accordance withone or other of said U.S. Pat. Nos. 3,947,807 and 3,984,806.

The electro-magnetic energy may be ultra-sonic, but, preferably this isof radio frequency and preferably of microwave frequency.

Said means for illuminatng the surface over which the vehicle is totravel with electro-magnetic energy may comprise a separate source ofenergy for reflection from each of said points on said surface, but,preferably a single source of electro-magnetic energy is utilized inorder to ensure coherence.

Preferably said single source of energy comprises a gun diode microwaveoscillator connected to feed a transmission port directed at saidsurface.

Preferably means are provided for determining the difference betweensaid two Doppler frequency components in order to provide an indicationof the extent of any turn and means are provided for detecting the signof said difference in order to indicate the direction of any turn inrelation to the heading of the vehicle.

Means may also be provided for detecting when said difference is zero,or substantially so, in order to provide an indication that the vehicleis travelling in a straight-ahead position.

Normally, each Doppler frequency component is converted to a voltage ina frequency-to-voltage converter prior to said difference beingdetermined and a voltage difference detector is provided to compare thetwo Doppler frequency representative voltages and provide a voltageoutput which is representative of said difference.

Means may be provided for shaping one of said Doppler frequencycomponents and counting the individual waves thereof to provide anindication of the mean distance travelled by the vehicle. When thearrangement forms part of a system as disclosed in either of ourco-pending applications mentioned above, normally this counter would bearranged to be reset to zero at each junction in the system.

Preferably means are provided for feeding, via a 90° phase shifter, aportion of the electro-magnetic energy received by one of said receivingmeans to a further means for deriving the Doppler frequency componenttherein and phase comparator means having one input derived from saidfurther Doppler frequency component deriving means and a second inputderived from that one of said first-mentioned two Doppler frequencycomponent deriving means which is associated with that one of thereceiving means, whereby said last-mentioned phase comparator providesone output signal if said vehicle is travelling in a forward directionand a different output signal if said vehicle is travelling in a reversedirection, in dependence upon the phase relationship of the signals atits input.

When fitted to a land vehicle, preferably at least the transmitting andreceiving ports are mounted on an unsprung part of the vehicle. In thecase of a conventional motor car, the whole apparatus may be mounted onthe back axle thereof, in which case a transmitting port forelectro-magnetic energy to illuminate the road surface is so directedthat the center of the radiation pattern illuminating said road surfacelies approximately 2 ft. in advance of said rear axle.

The invention is illustrated in and further described with reference tothe accompanying drawing in which,

FIG. 1 schematically represents the position of an equipment inaccordance with the present invention when fitted to a typical motorcar,

FIGS. 2 and 3 show in greater detail the equipment mounted on the rearaxle of the vehicle in order to indicate the directivities of theelectro-magnetic energy output and input ports

and FIG. 4 is a block schematic diagram showing the circuit componentsof one example of the equipment.

Referring to FIGS. 1 to 3, the equipment has a housing 1 which ismounted on the rear axle 2 of the vehicle. A first transmission port 3is provided to transmit electro-magnetic energy in a flood beam towardsthe road surface such that the center of the energy pattern contacts theroad surface at a point approximately 2 ft. in front of the rear axle 2.The electro-magnetic energy inlet ports 4 and 5 are provided to receiveelectro-magnetic energy returned from the road surface. This returnedelectro-magnetic energy will contain a Doppler component which isdependent upon the relative velocity of that portion of the road surfaceto which the particular input port 4 or 5 is directed. As represented,inlet port 4 is directed to receive energy from a portion of the roadsurface in front of the axle 2 and to the right hand side (lookingforward) of the centre of the energy pattern originating from outletport 3. Inlet port 5 is directed to receive energy from a portion of theroad surface in front of the axle 2 and to the left hand side (lookingforward) of the centre of the energy pattern originating from port 3. Inother words ports 4 and 5 receive energy reflected from portions ofilluminated surface on either side of a line extending along the lengthof the vehicle. The inclination of the main directivities of the ports 4and 5 with respect to said line is not critical, but will commonly be ofthe order of 45°, in the horizontal plane. The depression of the ports 4and 5 is such that again the portions of surface looked at by each isapproximately 2 ft. in front of the axle.

As has already been mentioned the electro-magnetic energy received bythe ports 4 and 5 will contain a Doppler frequency component which isdependent upon the velocity of that portion of the road towards whichthe particular port is directed. When the vehicle is travelling in astraight line, the Doppler components received by each port 4 and 5 willbe sensibly equal. If, however, the vehicle engages in a right handturn,the Doppler frequency component in the energy received by port 5 will begreater than that present in the energy received by port 4 to an extentdependent upon the rate of turn. The reason for this is that therelative velocity of the portion of road surface to which port 5 isdirected is greater than that of the portion of road to which port 4 isdirected when the vehicle is engaged on a right hand turn.

From the Doppler information thus derived, data signals may be developedwhich represent firstly the mean velocity of the vehicle, secondly therate and direction of turn of the vehicle and thirdly the generaldirection of the vehicle, i.e. forwards and backwards. One circuitarrangement for deriving these data signals will now be described withreference to FIG. 4.

Referring to FIG. 4, the ports 3, 4 and 5 of FIG. 3 are represented bythe correspondingly numbered blocks in FIG. 4. The flood beam providedby port 3 is derived from a gun diode microwave oscillator 6. Energyreturning from the road surface and received by port 4 is mixed in amixer 7 with a portion of the output of the oscillator 6 to provide, atthe output 8 of the mixer 7, a Doppler frequency which is related to therelative speed of the portion of road to which port 4 is directed.Similarly, energy received by port 5 is mixed in a mixer 9 with aportion of the output of oscillator 6, so that, at the output 10 ofmixer 9, a Doppler frequency is provided which is related to therelative velocity of the portion of road surface to which the port 5 isdirected.

Energy received by port 4 is also connected through a 90° phase shifter11 to a further mixer 12 to be mixed with a portion of the output ofoscillator 6. The Doppler signal at the output 13 of mixer 12 will besimilar in frequency to that at the output 8 of mixer 7, but the phaseof the signal at 13 will either lead or lag the phase of the signal at 8in dependence upon whether the vehicle is travelling in a forward or areverse direction. The phases of the signals at 8 and 13 are arranged tobe compared in a phase comparator 14 which provides an output toterminal 25 if the relative phase indicates reverse motion and an outputto terminal 26 if the relative phases indicate forward motion.

The outputs 8 and 10 of mixers 7 and 9 are connected to respectivefrequency to voltage converters 15 and 16 which in turn are connected toa voltage difference detector 17, the output of which will vary inmagnitude in dependence upon the degree of turn and the sign of whichwill depend upon whether the turn is to the left or to the right. Theoutput of voltage difference detector 17 is connected to a zero detector18, a sign detector 19 and an analogue to digital converter 20, which inturn are connected respectively to output terminals 21, 22 and 23. Zerodetector 18 will provide an output signal to terminal 21 when differencedetector 17 detects that the voltage outputs of converters 15 and 16 areequal, or substantially so, so that an output signal at terminal 21indicates that the vehicle is travelling straight ahead. Sign detector19 detects the sign of the output of difference detector 17 and appliesa digital signal to terminal 22 which indicates the direction of turn.Analogue to digital converter 20 applies a digital signal to terminal23, which indicates the magnitude of the output of difference detector17 and thus the degree of turn.

Doppler frequency at the output 10 of mixer 9 is also applied to asignal shaper 24 which shapes the waveform such that the individualwaves may be counted by a counter 25, which counter is connected toapply a digital signal representing its count (and hence mean distancetravelled) to a terminal 27.

It will be appreciated, therefore, that at terminals 25, 26, 21, 22, 23and 27 will appear signals which indicate whether the vehicle istravelling forward or backwards, whether the vehicle is turning or not,and if turning the direction of turn and the extent of the turn, andmean distance travelled. This information may be processed in a mannersimilar to that disclosed in said U.S. Pat. No. 3,984,806 in order toprovide for transmission to a base station and/or for display in thevehicle data concerning the position of the vehicle to which theequipment is fitted along a given network of routes.

The fact that the equipment is mounted on the rear axle of the vehiclemeans that the distance between the ports 3, 4 and 5 and the groundgenerally remains constant. Even if no axle is present, wheneverpossible at least the ports 3, 4 and 5 should be mounted on an unsprungpart of the vehicle.

I claim:
 1. An apparatus for deriving information concerning themovements of a surface-borne vehicle comprising means for illuminatingthe surface over which the vehicle is to travel with electro-magneticenergy, means for receiving reflected electro-magnetic energy from aportion of said illuminated surface to one side of a line extendingalong the length of said vehicle, means for receiving electromagneticenergy from another portion of said illuminated surface to the otherside of said line, means for deriving the Doppler frequency componentsin the energy received by each receiving means, means for utilizing saidtwo Doppler frequency components to provide information concerning themovement of said vehicle over said surface, means provided for feeding,via a 90° phase shifter, a portion of the electro-magnetic energyreceived by one of said receiving means to a further means for derivingthe Doppler frequency component therein and phase comparator meanshaving one input derived from said further Doppler frequency componentderiving means and a second input derived from that one of saidfirst-mentioned two Doppler frequency component deriving means which isassociated with that one of the receiving means, whereby saidlast-mentioned phase comparator provides one output signal if saidvehicle is travelling in a forward directon and a different outputsignal if said vehicle is travelling in a reverse direction, independence upon the phase relationship of the signals at its input.